Inhibition of the oxygen reduction reaction on copper with cobalt, cerium, and molybdate ions

The inhibition of the oxygen reduction reaction (ORR) on copper was investigated after pretreatment with Co, Ce, and Mo ions at applied potential simulating galvanic coupling to AA2024-T3. Specifically, the effect of Ce(III), Co(II), and MoO42- pretreatments on ORR was investigated in the mixed charge transfer, mass transport regime in pH 7-11 solutions using the Koutecky-Levich approach. Co reduces the ORR rate the most in more alkaline solutions (pH 9.5) while the Ce pretreatment works best in slightly less alkaline solutions (pH 7-8.2). Mo pretreatment was also most effective at pH 8.2 and was ineffective at pH 11. These results were consistent with chemical precipitation of Co(OH)(2) and Ce(OH)(3) or CeO2. MoO2 was rationalized to be formed by electrochemical reduction of MoO42- on copper. This process was not operative at highly alkaline pH at applied potentials near the open circuit potential of AA2024-T3. (c) 2005 The Electrochemical Society.